There are many companies that are doing very well with their App Store endeavors. One of the most successful app makers is Tapulous. Tapulous is the company behind the popular iPhone game called TapTap Revenge.

The game is a music game similar to Rock Band or Guitar Hero where the player taps glowing orbs as they reach the bottom of the screen to keep the rhythm going. Tapulous' game TapTap Revenge has been installed more than 20 million times with more than 600 million games played reports Reuters.

The game is said to be installed and in use on about 1/3 of the iPhones on the market. Tapulous claims that it is now making about $1 million per month off the App Store and based on its success the developer has raised $2.8 million from investors. The money Tapulous makes comes from ads, some of its premium games, and from selling songs via its games.

In April, Apple announced that the billionth download had been made from the App Store. While apps are being downloaded in large quantities by users, the App Store approvals process for developers has drawn criticism.

Some developers are walking away from developing apps for the store. The highest profile defection was the developer behind the Facebook app, Joe Hewitt. Consumers have also complained that the App Store needs a way to give refunds on apps. Competing application stores from other vendors allow the user to get a refund within a certain period if the app doesn't meet their standards.